Date of Completion

Spring 5-1-2023

Thesis Advisor(s)

Ashis Basu; Andrei Alexandrescu

Honors Major

Molecular and Cell Biology

Disciplines

Bacteria | Biochemistry | Cancer Biology | Genetics

Abstract

Bacteria, such as Escherichia coli, have an inducible system in response to DNA damage termed the SOS response. This system is activated when the replicative DNA polymerase (Pol) III encounters a lesion, uncouples from DNA helicase, and single-stranded DNA (ssDNA) accumulates at the replication fork. In this study, we investigated DNA-peptide crosslink (DpC), a common lesion that results from cross-linking of proteins or peptides, UV irradiation, and alkylating agents. To increase survival following formation of a lesion, the SOS response can utilize homologous recombination, translesion synthesis (TLS), or excision repair. With TLS, the levels of DNA Pol II, IV, and V increase to bypass the lesion and continue DNA replication. However, DNA Pol II, IV, and V are low fidelity polymerases resulting in error-prone replication and increased mutagenicity. In my work described here, the TLS efficiency and mutation frequency were compared among E. coli cells in the presence (+SOS) and absence (-SOS) of SOS response. E. coli cells were given two different sequences, CXG and CXT, with a single DNA- peptide crosslink (DpC) damage. The mutation frequency and TLS efficiency for both CXT and CXG was higher in the +SOS than the -SOS cells. In -SOS CXT and + SOS CXT, deletions were the most common mutation. In contrast, in -SOS CXG a greater number of G → T mutations were detected, whereas +SOS CXG exhibited a greater number of G → C mutations.

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